Metabolic activation of 1,1-dichloroethylene by mouse lung and liver microsomes

1987 ◽  
Vol 65 (7) ◽  
pp. 1496-1499 ◽  
Author(s):  
P. G. Forkert ◽  
M. Hofley ◽  
W. J. Racz
Keyword(s):  
Carbon Monoxide ◽  
Covalent Binding ◽  
Liver Microsomes ◽  
Metabolic Activation ◽  
Reactive Metabolites ◽  
Mouse Lung ◽  
Nonspecific Binding ◽  
Liver Necrosis ◽  
Isolated Lung ◽  
Cytochrome P 450

1,1-Dichloroethylene (1,1-DCE) causes lung and liver necrosis in mice. Covalent binding of [14C] 1,1-DCE to isolated lung and liver microsomes from CD-1 mice required NADPH and was strongly inhibited by carbon monoxide. Lung and liver microsomes isolated from animals treated with phenobarbital demonstrated no changes in covalent binding of [14C]1,1-DCE compared with those from vehicle-treated animals. While 3-methylcholanthrene caused no alterations in binding to lung microsomes, the same pretreatment resulted in significantly increased levels of binding to liver microsomes. Piperonyl butoxide caused significant decreases in covalent binding to lung and liver microsomes; SKF 525-A significantly inhibited binding to liver microsomes but had no effect on lung microsomes. The incubation of liver microsomes with inhibitors required more NADPH than those performed with lung microsomes. The results demonstrate that reactive metabolites of 1,1-DCE can be formed by lung and liver microsomes, and suggest the involvement of cytochrome P-450 isozymes in the lung and liver injury induced by the halocarbon. However, metabolic activation by lung and liver microsomes may additionally involve non P-450 dependent mechanisms as evidenced by relatively high levels of nonspecific binding of 1,1-DCE.

The role of metabolic activation by cytochrome P-450 in covalent binding of VP 16-213 to rat liver and HeLa cell microsomal proteins

1985 ◽  
Vol 21 (9) ◽  
pp. 1099-1106 ◽  
Author(s):  
J.M.S. van Maanen ◽  
C. de Ruiter ◽  
J. de Vries ◽  
P.R. Kootstra ◽  
F. Gobas ◽  
...  
Keyword(s):  
Hela Cell ◽  
Rat Liver ◽  
Covalent Binding ◽  
Metabolic Activation ◽  
Cytochrome P 450

Metabolic activation of a protein pyrolysate promutagen 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline by rat liver microsomes and purified cytochrome P-450

1988 ◽  
Vol 9 (1) ◽  
pp. 105-109 ◽  
Author(s):  
Yasushi Yamazoe ◽  
Medhat Abu-Zeid ◽  
Shunichi Manabe ◽  
Seiji Toyama ◽  
Ryuichi Kato
Keyword(s):  
Rat Liver ◽  
Liver Microsomes ◽  
Metabolic Activation ◽  
Rat Liver Microsomes ◽  
Cytochrome P 450

scholarly journals Metabolic activation of acetylenic substituents to derivatives in the rat causing the loss of hepatic cytochrome P-450 and haem

1978 ◽  
Vol 174 (3) ◽  
pp. 853-861 ◽  
Author(s):  
Ian N. H. White
Keyword(s):  
Covalent Binding ◽  
Metabolic Activation ◽  
Microsomal Protein ◽  
Significant Loss ◽  
Microsomal Cytochrome ◽  
Rf Values ◽  
Green Pigments ◽  
Cytochrome P 450

1. A number of acetylenic-substituted steroidal and non-steroidal compounds, including 2,2-dipropargylacetamide, pregna-2,4-dien-20-yno[2,3-d]isoxazol-17-ol (Danazol) and acetylene gas, when administered to rats in vivo brought about a decrease in the concentrations of hepatic microsomal cytochrome P-450 and haem. Abnormal haem-breakdown products, ‘green pigments’, and porphyrins accumulated in the livers of these animals. 2. For loss of microsomal cytochrome P-450 to occur in vitro, metabolic activation of the acetylenic substituent was necessary. The enzyme system responsible required NADPH and air, and was induced by pretreatment of rats with phenobarbitone; these are characteristics typical of the microsomal mixed-function oxidases. 3. When rats were dosed with 17α-ethynyl-17β-hydroxyandrost-4-en-3-one (ethynyltestosterone, 1mmol/kg) the pattern of green pigments extracted from the liver 4h after dosing and separated by t.l.c. was quite different from that in rats given 17β-hydroxy-17α-vinylandrost-4-en-3-one (vinyltestosterone), suggesting that reduction of the unsaturated triple bond to a double bond is not normally part of the metabolic activation pathway of the acetylenic substituent. 4. The green pigments extracted from the livers of rats 4h after the administration of the acetylenic-substituted compounds (1mmol/kg) when separated by silica-gel t.l.c. had variable RF values. The number and distribution of green pigments was characteristic for each compound examined. There was little correlation between the total loss of hepatic microsomal haem and the apparent intensity of the green pigments seen on the thin-layer chromatograms. 5. After incubation of [14C]acetylene in vitro with microsomal preparations from phenobarbitone-pretreated rats and a NADPH-generating system, no significant covalent binding to microsomal protein was detected over a 30min incubation period, although under similar conditions there was a significant loss of cytochrome P-450.

The characteristics of the microsomal hydroxylation of tolbutamide

1991 ◽  
Vol 69 (3) ◽  
pp. 400-405 ◽  
Author(s):  
Pierre M. Bélanger ◽  
Serge St-Hilaire
Keyword(s):  
Carbon Monoxide ◽  
Liver Microsomes ◽  
Hepatic Metabolism ◽  
Species Variation ◽  
Rat Liver Microsomes ◽  
Hydroxylase Activity ◽  
Microsomal Metabolism ◽  
Microsomal Hydroxylation ◽  
Cytochrome P 450

The in vitro metabolism of tolbutamide to the hydroxymethyl derivative was studied using hepatic microsomal homogenates. The hydroxymethyl metabolite was quantitated by HPLC. The hepatic microsomal hydroxylase was completely inhibited by carbon monoxide and was NADPH dependent. Metyrapone, α-naphthoflavone, phenelzine, mercuric chloride, and nitrogen significantly inhibited the reaction indicating the involvement of the cytochrome P-450 monooxygenase. Species variation showed that the order of hepatic microsomal activity was rat > rabbit >> guinea pig >> mouse and hamster. The reaction increased with time up to 40 min and followed Michaelis–Menten kinetics in rat liver microsomes with apparent Km and Vmax values of 224.4 μM and 359.9 pmol∙mg−1∙min−1, respectively. The reaction was induced by phenobarbital but was depressed after pretreatment with 3-methylcholanthrene and isosafrole. However, expression of the hydroxylase activity per nanomoles of cytochrome P-450 showed that the activity was much higher in liver microsomes of isosafrole pretreated rats. These results indicate the involvement of different isozymes of cytochrome P-450 in the microsomal hydroxylation of tolbutamide.Key words: tolbutamide metabolism, tolbutamide hydroxylation, microsomal hydroxylation, microsomal metabolism of tolbutamide, hepatic metabolism of tolbutamide.

Cytochrome P-450 dependent metabolic activation of 1-naphthol to naphthoquinones and covalent binding species

1985 ◽  
Vol 34 (13) ◽  
pp. 2261-2267 ◽  
Author(s):  
Mary d'Arcy Doherty ◽  
Richard Makowski ◽  
G.Gordon Gibson ◽  
Gerald M. Cohen
Keyword(s):  
Covalent Binding ◽  
Metabolic Activation ◽  
Cytochrome P 450

scholarly journals Metabolic activation of acetylenes. Covalent binding of [1,2-14C]octyne to protein, DNA and haem in vitro and the protective effects of certain thiol compounds

1984 ◽  
Vol 220 (1) ◽  
pp. 85-94 ◽  
Author(s):  
I N H White ◽  
J B Campbell ◽  
P B Farmer ◽  
E Bailey ◽  
N H Nam ◽  
...  
Keyword(s):  
Time Course ◽  
Covalent Binding ◽  
Protoporphyrin Ix ◽  
Metabolic Activation ◽  
Protective Effects ◽  
Trans Isomers ◽  
Thiol Compounds ◽  
Microsomal Hydroxylation ◽  
Cytochrome P 450

[1,2-14C]Oct-l-yne was used to investigate metabolic activation of the ethynyl substituent in vitro. Activation of octyne by liver microsomal cytochrome P-450-dependent enzymes gave intermediate(s) that bound covalently to protein, DNA and to haem. The time course and extent of covalent binding of octyne to haem and to protein were similar. However, two different activating mechanisms are probably involved. Whereas covalent binding to protein or to DNA was inhibited by nucleophiles such as N-acetylcysteine, that to haem was little affected. When N-acetylcysteine was included in the reaction mixtures, two major octyne-N-acetylcysteine adducts were isolated and purified by high-pressure liquid chromatography. G.l.c.-mass spectrometry and n.m.r. suggest that these are the cis-trans isomers of S-3-oxo-oct-1-enyl-N-acetylcysteine. Oct-1-yn-3-one reacted non-enzymically with N-acetylcysteine at pH 7.4 and 37 degrees C with a t1/2 of about 6 s also to yield S-3-oxo-oct-l-enyl-N-acetylcysteine. The same product was formed when microsomal fractions were incubated with oct-1-yn-3-ol, N-acetylcysteine and NAD(P)+. Octyn-3-one did not appear to react with haem or protoporphyrin IX. 5. A mechanism for the metabolic activation of oct-1-yne is proposed, consisting in (a) microsomal hydroxylation of the carbon atom alpha to the acetylenic bond and (b) oxidation to yield octyn-3-one as the reactive species.

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